The National Highway Traffic Safety Administration said on Monday it is opening a probe into 1.4 million Honda vehicles after reports of serious engine issues.

Honda in November 2023 recalled 249,000 vehicles in the United States with a 3.5 liter V6 engine after the Japanese automaker said a manufacturing defect in the engine crankshaft could cause the connecting rod bearing to prematurely wear and seize, leading to engine failure.

The U.S. auto safety agency said it has 173 reports of the issue in various Honda and Acura vehicles from the 2016-2020 model years. NHTSA's probe is to determine the severity of the issue and to determine if the vehicles not included in the 2023 recall should be covered.

Honda said Monday it was aware of the probe and "has already been in communication with the agency on this topic and will continue to cooperate with the NHTSA through the query process."

Honda first opened an investigation into the issue in 2020 and spent several years investigating before it announced a recall.

The automaker said last year it had 1,450 warranty claims tied to the recall. Under the recall, dealers are inspecting the vehicles will repair or replace the engine if needed.

NHTSA said all of the 173 reports "display failures that have characteristics consistent with those addressed" in the 2023 recall but are not covered.

The investigation covers 2016-2020 model year Acura MDX, 2018-2020 Acura TLX, 2016-2020 Honda Pilot, 2017-2019 Honda Ridgeline and 2018-2020 Honda Odyssey vehicles.